1. Field of the Invention
The present invention relates to a playback device which plays back a plurality of data which are stored on a recording medium such as an optical disc or optomagnetic disc and, more particularly, to an improved data playback device that ensures a constant uninterrupted output of data to be played.
2. Description of Related Art
In the past, compact disc (referred to simply as CD hereinbelow) players which play back CDs have become widespread as such playback devices.
However, in recent years mini discs (referred to simply as MDs hereinbelow) have also become widespread, and these not only play back recorded data, in the same way as CDs, but also have a recording medium whereby data can be rewritten.
In these MDs, optical discs or optomagnetic discs are housed in protective cassettes. There are two types of MD. These are the premastered type in which optical discs are housed in protective cassettes and which perform playback only, and the recordable type in which an optomagnetic disc is housed in a protective cassette and which are configured such that data can be written onto a recording medium.
With recordable-type MDs, if data are repeatedly recorded and erased, certain tracks on the recording medium will become divided into a plurality of parts. A description will be given, with reference to FIG. 1, of the degree to which a plurality of parts are generated in this way on a single track. This figure is an explanatory diagram showing a state in which a plurality of data recorded on a disc are expressed linearly. It should be noted that, unless otherwise indicated to the contrary, the term "disc" refers to these recordable-type MDs.
As shown in FIG. 1(a), data in track 1 through track 6 are stored on the disc. If the data recorded in tracks 2, 4 and 6 are erased, then, as shown in FIG. 1(b), the regions of tracks 2, 4 and 6 become regions in which data are not recorded, in other words, blank regions (indicated on the diagram by diagonal lines).
The track numbers for the data remaining in tracks 1, 3 and 5 are then altered such that they are each closed up, as shown in FIG. 1(c), with the blank regions remaining unaltered. In other words, the numbers are altered such that track 1 remains the same, track 3 becomes track 2 and track 5 becomes track 3.
If a new track, for example a track 4 which is configured with a relatively large amount of data, is then stored on the disc in the state shown in FIG. 1(c), then the data in said track 4 are stored so as to fill up from the front the blank regions shown in FIG. 1(c), and the data in track 4 which is stored in these blank regions consist of parts 1, 2 and 3, as shown in FIG. 1(d). In other words, the data recorded as the data in track 4 are divided and recorded in a plurality of discontinuous parts. It should be noted that a TOC (Table Of Contents), and a user TOC (User Table Of Contents, referred to simply as "UTOC" hereinbelow) which are identification data recording the start address and end address of each track and each part are stored on the disc.
An MD player is generally used to read out and play back data recorded on an MD. A case will now be assumed in which readout and playback are performed on a disc in a state such as that shown in FIG. 1(d), using an MD player. If, as shown in FIG. 2, an optical pickup 11 begins to read data from a part neighboring the end address of part 1 of the song data in the fourth track, then when the amount of data read from this neighboring part and stored in RAM (Random Access Memory), which is used as a storage device, reaches a specified amount N, playback of the data stored in the RAM begins, in conjunction with the reading and storing of data. At this time, when the end address (2) of the part is reached after data readout has started, the pickup must jump to the start address (3) of part 2. When this jump takes time to occur, there is a problem that data in the RAM 15 may be used up before the jump has been completed and reading of data from the next part has commenced, in other words, there is no data in the RAM, there is thus no data to be played back and no sound is produced for a moment.